Bulk bags, also known as semi-bulk containers, are used for the storage and transportation of liquids and dry flowable materials as well as viscous semiliquids such as gels and resins. The bags are typically constructed from high strength woven polyolefin fabric allowing the storage of very dense and heavy materials. Standard bulk bags are either cubically or cylindrically shaped with a volume of approximately 27 cubic feet and typically hold around 2,000 pounds of material. One of the advantages of cubically shaped bulk bags over other types of storage containers such as barrels is that, the bags can be stacked so as to take up a minimum of storage space.
Because of the great weight of bulk bags when they are full, fork lift machines or hoists must be used to carry the bags from place to place as well as hold the bags when the bag contents are to be discharged, typically into a mixing vat or another bag. Most bulk bags are, therefore, designed to be carried with a fork lift and have slings in the upper four corners for that purpose. After maneuvering the fork lift in front of the bulk bag, the tines of the fork lift are raised to a level just above the height of the bag. The fork lift is then advanced forward so that the tines travel over the top of the bag. At the same time, the corner slings must be held so that the tines are inserted therethrough. The bulk bag may then be lifted and carried by the fork lift with the bag hanging by two corner slings on each side looped around one of the two tines of the fork lift. Loading a bulk bag onto a fork lift in the manner described above typically requires three persons, one to drive the fork lift and one on each side of the bag to align the corner slings with the advancing fork lift tines.
Once the bulk bag has been placed under onto the fork lift tines, the bag may be carried to the location where its contents are to be discharged. The bag is then placed by the fork lift directly over the discharge container (e.g., a mixing vat) and the bottom of the bag is opened. In the case of thin liquids, a preformed spout in the bag may be employed which can be opened and closed manually. With more viscous contents, however, the bag opening is typically accomplished by simply cutting the bottom of the bag with a knife in order to create a large enough opening. The bag contents in either case are then allowed to empty into the discharge container due to the force of gravity. In the case of gelled viscous liquids, several minutes may elapse before the bag is completely empty even with a relatively large opening. Heretofore, in the case of very viscous contents, there has been no practical way to discharge anything but the entire contents of a single bulk bag into one particular discharge container. That is, once a bulk bag is opened, there has been no way to seal the bag after a certain amount of contents have been discharged. The weight and viscosity of the gelled semiliquids typically stored in bulk bags make it impossible for the discharge flow to be stopped manually. Thus, users of bulk bags have simply had to adjust their processes so as to accommodate the entire contents of a bulk bag at a one particular discharge container. It would be advantageous, however, if there were to be a way by which bulk bag users could controllably discharge the contents of bulk bags. A plurality of discharge containers could then each receive the partial contents of any one bulk bag.